The present invention relates to a sounder, which is used for producing a "ringer sound" by reproducing a specific frequency band-width. The sounder is built in various mobile communication apparatuses.
A conventional sounder is depicted in FIG. 4A and FIG. 4B. FIG. 4A is a plan view of a conventional sounder, and FIG. 4B is a cross sectional view of the same sounder.
A ring-shape magnet 21 is formed by injection molding a resin magnet. A plate 22 is formed by an insert mold at the same time as when the ring-shape magnet 21 is produced by injection molding. The plate 22 has a center pole 23, a hole 24 for leading out the ends of a coil 26, and a hole 25 for providing the back side of the sounder with an opening.
The coil 26 is laid around the center pole 23 of the plate 22. Each end of the coil 26 is pulled out from the hole 24 of the plate 22, and connected to an electrode of a printed circuit board 27, which board is coupled to the back side of the plate 22. A diaphragm 28 is disposed on the magnet 21 to cover an outer periphery of the magnet 21 so that a uniform magnet gap 29 can be provided between the diaphragm 28 and an upper face of the center pole 23.
A resonant cover 30 is connected to the outer periphery of the magnet 21 so that the upper side of diaphragm 28 can be blocked. The resonant cover 30 comprises a hole 31 on a side thereof for releasing sound, and an air chamber 32 above the diaphragm 28. A terminal 33 is soldered to the resonant cover 30 through a hole punched in the printed circuit board 27.
A rectangular wave signal is applied to the coil 26 via the terminal 33 of the conventional sounder of the above structure, and thereby produces a magnetic field through a magnetic circuit comprising the magnet 21 and the plate 22. The magnetic force produced by this magnetic field draws the diaphragm 28, which is made of high permeable material such as permalloy, toward the center pole 23 of the plate 22 so that the diaphragm 28 is attracted to the upper surface of the center pole 23. Thus, the diaphragm 28 becomes deflected.
Since a rectangular wave signal is applied to the coil 26, the diaphragm 28 deflects and then restores repeatedly, thereby reproducing a specific sound of frequency bandwidth. However, there are problems with the conventional sounder. For instance, the coil 26 is not wound directly around the center pole 23. Rather, the coil 26 is wound by a separate process, and then placed around the center pole 23. However, first, both ends of the coil 26 have to be pulled out through the same hole 24 to the back side of the printed circuit board 27. Then, the coil 26 is positioned around the outside of center pole 23, and glued to the center pole. Each end of the coil 26, which has been pulled out to the back side of the plate 22, is then connected with an electrode on the printed circuit board. Then, the terminal 33 is connected with an electrode on the printed circuit board.
As described above, too many components and steps are required to form, position and mount the coil 26 in a specified place, and to be connect the ends of the coil to the backside of the sounder. As a result, the process of assembling the sounder is not very efficient, and can easily result in a sounder that malfunctions.
For example, when connecting the ends of the coil 26 to printed circuit board, the electrodes may be connected with a wrong polarity. Or, the adhesive used in gluing the coil 26 to the center pole may touch the diaphragm 28, and cause the sounder to malfunction.
The present invention intends to solve such problems with a high quality sounder that is assembled with fewer components and steps. The sounder, according to the present invention, is small and slim, and yet is capable being assembled with high efficiency.